Evaporation of potentially explosive residue of oxygen containing gas fractionation process

ABSTRACT

LOW-BOILING POINT LIQUIDS ARE EVAPORATED IN AN EVAPORATING STREAM FORMED BY ENTRAINING AMBIENT AIR IN A JET OF PROPELLANT GAS. THE LIQUID TO BE EVAPORATED IS ATOMIZED BY INJECTION INTO THE JET AND AN AEROSOL IS THEREBY FORMED. THE ATOMIZED LIQUID IS CONTINUOUSLY EVAPORATED IN THE THUS FORMED AEROSOL STREAM BY HEAT DERIVED FROM THE CHANGE OF ENTHALPY OF THE AMBIENT AIR AND PROPELLANT GAS.

Nov. 9, 1971 L. SETZPFANDT ETA!- Filed July 16. 1968 CONTAINING GASFRACTIONATION PROCESS 3 Sheets-Sheet l Air 7 E 5 71' r/ i FRACTIONATIONCOLUMN 74 Potentially explosive fractionation residue 10 Air GaseousPropellant INVENTORS LOTHAR SETZPFANDT J 0581' STOCKNER iliiwfi adATTORNEY NOV. 9, 1971 SETZPFANDT EIAL 3,618,332

EVAPORATION OF POTENTIAL-LY EXPLOSIVE REsmuE 0F OXYGEN CONTAINING GASFRACTIONATION PROCESS Filed July 16, 1968 5 Sheets-Sheet 2 INVKNTORSLOTHAR .SETZI' PANIYI JOSE!" STOCKNKR ATTORNEY Nov. 9, 1971 1 zp -r ETAL3,618,332

EVAPORATION OF POTENTIALLY EXPLOSIVE RESIDUE 0F. OXYGEN CONTAINING GASFRACTIONATION PROCESS 3 Sheets-Sheet 5 Filed July 16, 1968 F I G 3INVENTORS LOTHAR SETZPFAND'I' JOSEF STOCKNER ATTORNEY United StatesPatent ice 3,618,332 Patented Nov. 9, 1971 US. CI. 62-18 5 ClaimsABSTRACT OF THE DISCLOSURE Low-boiling point liquids are evaporated inan evaporating stream formed by entraining ambient air in a jet ofpropellant gas. The liquid to be evaporated is atomized by injectioninto the jet and an aerosol is thereby formed. The atomized liquid iscontinuously evaporated in the thus formed aerosol stream by heatderived from the change of enthalpy of the ambient air and propellantgas.

This invention relates to a process and apparatus for the evaporation oflow-boiling point liquids.

Low-boiling point liquids can be evaporated without danger if they arefree from explosive substances, such as hydrocarbons. However, duringthe separation of gaseous mixtures containing even minor quantities ofexplosive substances admixed therewith which are enriched duringrectification, there is the constant danger of explosions in terferingwith the operation of the process at the points where solid depositionsof the explosive gases can collect. Acetylene accumulated in liquidoxygen during the separation of atmospheric air is an example of such asubstance.

When shutting down low-temperature gas separation plants, e.-g., airseparation plants, or the individual components of such plants,low-boling point liquids or solidliquid suspensions also remain in theapparatus as a residue. Such residue must be rapidly removed, safetlyevaporated and conducted away. One known method of disposing of suchresidue is to pass the liquid or suspension into a cement pit, normallydisposed in the ground near the plant. Under the influence of groundheat and heat from the surrounding atmosphere, the residual liquidgradually evaporates. The pit can also be filled with a heat-retainingmass for accelerating such evaporation. The low-boiling point liquidevaporates in the pit relatively slowly, and during this process isenriched in higher-boiling admixtures, particularly hydrocarbons. If thesolubility of the hydrocarbons in the liquid is exceeded, then it ispossible, for example, for acetylene to be precipitated in solid form inthe liquid oxygen and to lead to an explosion. Furthermore, the areasurrounding the pit is endangered by cold clouds of vapor, produced byevaporation, creeping along the ground. These clouds represent a gravedanger since they have, in part, a high oxygen content and they persistfor long periods of time, due to the slow evaporation process in thepit.

In order to preclude the aforedescribed danger of acetyleneprecipitating in solid form, it is known from German Pat. 1,033,689 toconcentrate liquid oxygen containing hydorcarbons from, for example, theexternal chamber of the main condenser of a double rectification column,by evaporation in the second evaporator only to such an extent that theconcentration of hydrocarbons in the residual liquid remains below theexplosion or solubility threshold. The residual liquid, rich inhydrocarbons, is separated from the gas after evaporation in the secondevaporator, in a separator, and is either withdrawn or purified inadsorbers. This process, however, is very expensive from the standpointof equipment cost. Furthermore, the liquid oxygen cannot be completelyevaporated in the second or additional evaporator, since, upon totalevaporation, the solubility threshold of the acetylene is certain to beexceeded, and acetylene would precipitate in solid form. The use of anadditional evaporator, as well as the subsequent purification of theresidual acetylene-rich liquid in regenerative adsorbers is alsocumbersome and dangerous, since, in both methods, a relative enrichmentof acetylene occurs.

SUMMARY OF THE INVENTION A principal object of this invention thereforeis to provide a process and apparatus therefor wherein low-boiling pointliquids, particularly liquids having hydrocarbons admixed therewith, canbe evaporated in a rapid, safe, and complete manner.

Upon further study of the specification and claims, other objects andadvantages of the present invention will become apparent.

The objects are attained in accordance with this invention, by drawingin atmospheric or ambient air by means of a jet or propellant gas andsimultaneously atomizing the liquid to be evaporated, whereupon theatomized liquid is continuously evaporated in a predeterminedconcentration in the thus-formed aerosol.

In accordance with the process of this invention, the kinetic energy ofa jet propellant gas exiting from a nozzel is utilized to simultaneouslyatomize the liquid to be evaporated and form an aerosol and to draw inand entrain a limited quantity of atmospheric or ambient air to form anevaporating stream. Thereafter, the atomized liquid is continuouslyevaporated in a predetermined concentration in the thus-forming aerosol,while the propellant gas and the drawn-in air is cooled. For producingthe evaporating stream, the aerosol is conducted through an evaporationchamber restricted in its lateral dimensions.

This process exhibits the advantage that, due to the atomization, thelow-boiling liquid evaporates rapidly and completely, and thereforeadmixed hydrocarbons present are not enriched in the liquid to beevaporated. The changes in enthalpy level of the entrained air and ofthe propellant gas provide the heat required to evaporate the atomizedliquid. In accordance with the invention, the aerosol has imparted to ita high flow velocity and turbulence in the evaporation chamber, and theimproved heat transfer rate from the propellant gas and the entrainedair to the atomized liquid allows the latter to evaporate quicklywithout residue.

When evaporating an oxygen-rich liquid, the propellant gas and thedrawn-in air decrease the oxygen concentration of the aerosol, whichdecrease is enhanced when the evaporated liquid leaves the evaporationchamber and mixes intimately with the surrounding air as a result of thecontinuing high kinetic energy of the exhausted vapors. Danger to thesurroundings of the site is thereby made impossible.

The liquid to be evaporated is introduced into the evaporation chamberunder pressure to atomize the liquid. The amount of liquid atomized bythe jet of propellant gas in increased with increasing liquid pressure.

In accordance with the invention, a preferred apparatus for conductingthe process comprises an evaporating chamber consisting of a mixing tubehaving centrally disposed at one end a propellant gas nozzle ofsubstantially smaller cross section, (e.g. 1.5 to 12%) than the tube. Atleast one liquid conduit is disposed substantially normal to the mixingtube and extends at its open end proximate the propellant gas nozzle. Inthe tube, turbulent flow and high flow velocity, e.g. about 19 to 300,preferably 65 to 230 meters/sec. of the aerosol are produced, due to thelarge amount of atmospheric air which is entrained by the srteam ofpropellant gas, and the stream of both gases together is driven throughthe mixing tube. The turbulent flow, in the mixing tube acts to rapidlytransfer the heat of the propellant gas and the entrained air to theatomized, cold liquid. The mixing tube should be of great enough lengthto provide substantial evaporation of the liquid before exhaust thereof.Tubes of a length between and 30 meters have been found suitable forthis purpose.

The attached drawings depict the preferred embodiment of the apparatusof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a longitudinalsection through an evaporating device by means of which the process ofthis invention for the evaporation of low-boiling liquids is con ducted,and

FIGS. 2 and 3 show modified arrangements of the apparatus shown in FIG.1.

The device according to FIG. 1 consists substantially of a verticallydisposed mixing tube 1. A propellant gas nozzle 2 having a nozzle end 3substantially smaller in cross-sectional area than the inside diameterof the mixing tube 1 is centrally disposed at the lower end of the tubeso that there is formed an annular opening 4 between the nozzle 2 andthe mixing tube 1. A liquid conduit 5 is disposed substantially normalto the propellant gas nozzle 2 penetrating the lower end of the mixingtube 1 at 6. The conduit has an open end 7 vertically coincident withthe inner wall 8 of the nozzle end 3 adjacent the point of penetration6. The propellant gas employed can be low-pressure air since such isavailable without cost and need only be brought to a higher pressure bymeans of a blower, which is, for example, usually present in airseparation plants. It should be understood, however, that under certaincircumstances, other fluids such, for example, as, preferablysuperheated, steam can be advantageously employed as the propellant gas.

The evaporation of a low-boiling liquid is conducted in accordance withthe invention, by drawing in a limited amount of atmospheric air,indicated by arrows 10, under the influence of a low-pressure air jet,shown by arrows 9, exiting the nozzle end 3; atomizingliquid-to-be-evaporated, indicated by arrow 11; and continuouslyevaporating the atomized liquid in an aerosol which is formed in themixing tube 1. Vapors, free of atomized liquid llezave the upper end ofthe mixing tube 1 shown by arrow The inside diameter and the length ofthe evaporation chambenor mixing tube must be adapted to the requiredevaporation rate of the atomized liquid. An annular space is formedbetween the centrally disposed propellant gas nozzle, and the inner wallof the end of the mixing tube is of such a size that a suflicient amountof atmospheric air is entrained into the mixing tube in order toevaporate the atomized liquid. The size of the annular opening isdictated by a requirement for an air velocity therethrough greater orequal to the entrainment velocity for the atomized liquid. The volume ofair drawn-in is a multiple of the volume of propellant gas, soproportioned that the change in enthalpy level of the drawn-in airsupplies the larger part of the heat of evaporation of the atomizedliquid.

Preferably, the mixing tube is disposed vertically and the propellantgas nozzle is arranged in the lower end of the mixing tube, so that theatomized liquid is carried in the aerosol flow from the bottom to thetop through the mixing tube. Dry gas exits at the upper end of themixing tube to be safely blown into the atmosphere at a great heightfrom the ground. The mixing tube, however,

4 can also be disposed horizontally, if so desired, in which case theend of the tube is turned upwardly. With such an arrangement, thehorizontally positioned tube requires more floor space than a verticallydisposed tube.

The lower end of the mixing tube can be straight or can have a flaredsection, preferably conical in shape. The flared construction of the endof the mixing tube will considerably enhance the intake of atmosphericair under the influence of the jet of propellant gas. A tube end ofconical configuration is also easily produced from the viewpoint ofmanufacturing technology.

The propellant gas nozzle is in the configuration of a Laval nozzle 2,thereby making supersonic flow possible.

The Laval nozzle, well known to those skilled in the art, ischaracterized by a converging-diverging nozzle wall, configured toprovide acceleration of fluids flowing therethrough into the supersonicregion. This ensures that, due to the high velocity of the propellantgas, as much atmospheric air as possible is entrained into the mixingtube and that the liquid to be atomized is converted in the mixing tubeinto an extremely fine, rapidly evaporating mist.

In the preferred embodiment, in order to impart supersonic speed to thepressurized air stream 9, the propellant gas nozzle 2 is constructed asa Laval nozzle with entrance and exit portions 16 and 17 respectively.

The liquid conduit 5 preferably enters the lower end of the mixingtube 1. The annular opening 4 for drawing in atmospheric air between thepropellant gas nozzle and the mixing tube is only slightly reduced bythe liquid conduit. The conduit can readily be attached to the wall ofthe mixing tube 1, such for example as by welding.

Advantageously, the liquid conduit 5 extends in as far as the inner wall8 of the nozzle end 3 at a point adjacent the point of penetration 6 ofthe conduit. In this manner, the jet of propellant gas exiting from thenozzle end is undisturbed by the liquid conduit. Since the jet ofpropellant gas 9 conically widens after leaving the nozzle 2, the end ofthe liquid conduit 7 is beveled. In this connection, the angle of theend with respect to the nozzle center line is larger than the angle ofthe jet cone, to facilitate the feeding of the liquid. The kineticenergy of the boundary layer of the gas jet is thus eflective over theentire width of the liquid conduit to atomize the liquid.

A suitable space 14, e.g. about 0.3 to 3 cm. is provided between thenozzle end 3 and the end 7 of the liquid conduit 5, since, whenatmospheric air is employed as propellant gas, water vapor and carbondioxide can freeze out of the air in the zone of the propellant gasnozzle, due to the cold of the liquid to be atomized. Such freezing isavoided by providing this heat-insulating spacing between the nozzle endand the liquid conduit.

In a particularly advantageous embodiment, several liquid conduits canbe arranged around the propellant gas nozzle so that the kinetic energyof the boundary layer of the gas jet can be utilized throughout itsentire circumference for the atomization of the liquid. Furthermore, inthis manner, a very evenly distributed gasliquid mixture is provided inthe mixing tube, so that the atomized liquid evaporates rapidly andcompletely.

The amount of atmospheric air drawn in by the jet of propellant gas canbe additionally increased, if so desired, by providing the upper sectionof the mixing tube with a diffuser 18 and a cylindrical, enlarged tube19 arranged thereafter, as it is shown in FIG. 2. The total length oftube 1, diffuser 18 and tube 19 approximately corresponds to the lengthof tube 1 in FIG. 1. The length of diffuser 18 and tube 19 is about 70to of that total length, and the angle of the diffuser 18 with respectto diffuser centerline is about 5 to 7. The area of the cross section ofthe tube 19 is given by the demand the velocity at the end of the tube19, indicated by the arrow 20, is about 15 to meters/sec.

According to FIG. 3, the propellant gas nozzle, if so desired, can be ofa continuously tapering shape. With such a nozzle 21, the maximumvelocity will be the velocity of sound reached in the mouth of thenozzle. The exit diameter of the nozzle 21 is about 10 to 30% of itsentrance diameter. It is advantageous, if the length of the nozzle 21corresponds to the length of the nozzle 2. Then the nozzles can easilybe exchanged. The exchangeability of the nozzles makes it possible touse one and the same apparatus in spite of different conditions, e.g.pressure, of the propellant gas.

In general, this invention is applicable to the rapid evaporation of anyliquid, but is particularly useful for the evaporation of liquids havinga temperature of 180 to 200 C., and especially those having aconcentration of potentially explosive hydrocarbons, such as acetylene.Consequently, liquid oxygen streams containing any acetylene therein (inpractice usually about to 2.l0 parts by weight of actylene in 100 partsby weight of oxygen) are advantageously treated by this invention toremove the explosive hazard.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and not lirnitativeof the remainder of the specification and claims in any way Whatsoever.

The following test results are applicable to an evaporating device ofthe present invention having the following configuration and operatingunder the following conditions (see FIG. 1):

Length of mixing tube 1: 5.5 m. Inner diameter of mixing tube 1: 100 mm.Angle of flared portion 13: 40 Length of flared portion 13: 120 mm.Laval nozzle 2:

External diameter: 48.3 mm. Throat diameter: 14.5 mm. Length of:

Entrance portion 16: 10 mm. Exit portion 17: 21 mm. Angle with respectto nozzle centerline of:

Entrance portion 16: 60 Exit portion 17: 5 Liquid conduit 5:

Diameter: 8 mm. Angle of end 7 with respect to centerline of nozzle 2:10 Distance across space 14: 3 mm. Ambient temperature: +5 C. to +10 C.Temperature in the Laval nozzle 2: C. to C.

EXAMPLE I Without liquid injection 150 Nm. /h. of propellant air, at apressure of 0.5 atmosphere gauge injected through the nozzle 2 drew inand entrained in the mixing tube 1,630 Nm. /h. of atmospheric air 10.The velocity of the drawn-in air in the annular opening 4, immediatelyprior to liquid injection, was 25 m./sec. After injection of the liquidnitrogen into the stream through the liquid conduit 5, the weight ratioof drawn-in air to propellant air decreased to 3.1, and the air velocityin the annular opening 4 was reduced to 18 m./sec. The weight ratio ofthe evaporated liquid to the propellant gas was 2.9. At the upper end ofthe mixing tube 1, a flow rate of 19 m./ sec. was observed at a gas exittemperature of -130 to 140 C.

6 EXAMPLE 11 Without liquid injection 600 Mm. /h. of propellant air at apressure of 5.5 atmospheres gauge drew in and entrained in the mixingtube 1,800 Nm. /h. of atmospheric air. The velocity of the drawn-in airin the annular crosssection, immediately prior to injection of liquid,amounts to 68 m./sec. After feeding liquid nitrogen into the streamthrough the liquid conduit 5, the weight ratio of drawn-in air topropellant air decreased to 2.3, and the air velocity in the annularcross-section to 47 m./sec. The weight ratio of evaporated liquid topropellant air was 2.5. A flow rate of 63 m./sec. and a gas exittemperature of l30 to C. resulted at the upper end of the mixing tube.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/ oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions. Consequently, such changes and modifications are properly,equitably, and intended to be within the full range of equivalence ofthe following claims.

What is claimed is:

1. In a process for the low temperature fractionation of anoxygen-containing gas wherein upon termination of said process, apotentially explosive low boiling point liquid is a residue of saidprocess, said residue comprising liquid oxygen and hydrocarbon, theimprovement which comprises evaporating said potentially explosiveliquid by:

forming an evaporating stream by entraining ambient air in a jet ofpropellant gas;

simultaneously atomizing said potentially explosive liquid residue byinjection into sad jet, thereby forming an aerosol;

whereby the atomized potentially explosive liquid residue is continouslyevaporated in the thus-formed aerosol stream.

2. Process according to claim 1, characterized in that the potentiallyexplosive liquid to be evaporated is under pressure.

3. Process according to claim 1, characterized in that low-pressure airis employed as the propellant gas.

4. Process according to claim 1, characterized in that steam is employedas the propellant gas.

5. Process according to claim 1, characterized in that said potentiallyexplosive liquid comprises oxygen and acetylene, and saidoxygen-containing gas is air.

References Cited UNITED STATES PATENTS 471,361 3/1892 Rogers 431-211728,140 5/ 1903 Spicer 43 l211 1,719,397 7/ 1929 Edwards 431-2112,043,597 6/1936 Sloyan 431211 2,918,901 12/1959 First 62-18 2,975,6063/ 1961 Karwat 62--18 NORMAN YUDKOFF, Primary Examiner A. F. PURCELL,Assistant Examiner US. Cl. X.R. 261-76; 431-211

